1. Field of the Invention
The present invention relates to a vehicle power unit configured to an internal combustion engine and a transmission device for transmitting rotation of an engine crankshaft to the wheels of the vehicle. More particularly, the present invention relates to a configuration of a lubricating system provided within the power unit.
2. Description of the Background Art
For stable operation of a power unit, which includes a transmission device which transmits the rotational driving power of the internal combustion engine to vehicle wheels, a vehicle is equipped with various types of auxiliary machinery including a lubricating system which feeds lubricating oil to the lubricating portions of shafts and gears of the engine. Such a power unit is shown, for example, in Japanese Patent Laid-open No. Hei 10-119591. The lubricating system generally includes an oil strainer installed in an oil storage portion disposed in a housing, and a feed pump for discharging the lubricating oil from the oil storage portion via the oil strainer.
According to Japanese Patent Laid-open No. Hei 10-119591, an oil strainer is attached to a lower portion of a crankcase, and the oil storage portion is formed in the lower portion of the crankcase. The crankcase is divided into two case-half bodies. One case-half body of the crankcase includes a recess formed therein adapted to receive the strainer therein. When the other case-half body of the crankcase is joined to the one case-half body, both the case-half bodies sandwich the strainer therebetween.
Further, according to Japanese Patent Laid-open No. Hei 10-119591, a power transmission device can establish a plurality of forward stages, a neutral stage and a reverse stage. Establishment of these speed change stages is achieved in response to a rotational position of a shift drum. The power transmission device includes a turn restricting mechanism which restricts the turn of the shift drum. The turn-restricting mechanism has a torsional coil spring and is provided to prevent the establishment of the reverse stage during forward travel of the vehicle. The inner wall surface of the housing is formed with a specifically dimensioned, to-be-engaged groove to retain an end of the torsional coil spring of the turn-restricting mechanism.
However, according to Japanese Patent Laid-open No. Hei 10-119591, in order to attach strainer to the power unit, it is necessary to join the other case-half body to the one case-half body with the strainer received in the recess of the one case-half body. Such attachment structure has the possibility that the strainer received in the recess of the one case-half body of the crankcase drops or becomes misaligned when the other case-half body is joined to the one case-half body. An increased dimensional accuracy is required in order to join the other case-half body to the one case-half body while preventing the drop (or misalignment) of the strainer. This may lead to a reduction in manufacturability of the power unit.
Moreover, to retain the torsional coil spring of the turn-restricting mechanism, the internal wall surface of the housing needs to be formed in a dedicated and/or properly dimensioned shape. This complicates the forming operation of the housing for disposing the power transmission device, which may lead to a reduction in manufacturability of the power unit.
In consideration of the above described problems, it is an object of the present invention to provide a power unit that improves the attachment performance of an oil strainer and enhances productivity of an internal combustion engine.